Polishing compound and method for polishing substrate

ABSTRACT

A polishing slurry and a polishing method which are suitably used in a CMP technique for flattening a surface of a substrate in a production process of a semiconductor device. The polishing slurry comprises particles and a medium in which at least a part of the particles are dispersed, wherein the particles are made of at least one of (1) a cerium compound selected from cerium oxide, cerium halide and cerium sulfide and having a density of 3 to 6 g/cm 3  and an average particle diameter of secondary particles of 1 to 300 nm and (2) a tetravalent metal hydroxide. A polishing method using the polishing slurry takes advantage of a chemical action of particles in the polishing slurry and minimizes a mechanical action of the particles, thereby achieving a decrease in scratches caused by the particles and an increase in polishing rate at the same time.

TECHNICAL FIELD

The present invention relates to a polishing slurry which is suitablyused in a technique for producing a semiconductor device and a method ofpolishing a substrate by use of the polishing slurry.

BACKGROUND ART

In a current production process of a ULSI semiconductor device,processing techniques for achieving a higher density and a higher degreeof integration are under study and development. As one of suchprocessing techniques, a CMP (Chemical Mechanical Polishing) techniquehas been gaining ground as a technique absolutely required forflattening of an interlayer insulating film, formation of shallow trenchisolation, and formations of plugs and implanted metal wiring, in aproduction process of a semiconductor device.

In a conventional production process of a semiconductor device, silica(SiO₂)-based particles and ceria (CeO₂)-based particles have been widelyused as abrasive of a CMP slurry for flattening an inorganic insulatingfilm layer such as a silicon oxide insulating film which is formed bysuch a method as plasma CVD or low pressure CVD. A representativeexample of the silica-based abrasive is fumed silica. The fumed silicais produced by dispersing particles which has been grown by such amethod as thermal decomposition of silicon tetrachloride, into a mediumand then adjusting the pH of the solution. Polishing of an insulatingfilm layer by use of a fumed silica abrasive has a problem that apolishing rate is low.

A representative example of the ceria-based abrasive is cerium oxide.The most outstanding feature of a cerium oxide abrasive is a highpolishing rate which cannot be achieved by the silica-based abrasive. Aceria-based compound having a high valence such as cerium oxide, asknown as a strong oxidizing agent, has a characteristic of beingchemically active. Thus, its chemical action as an oxidizing agent and amechanical removing action of particles interact with each other. It isbelieved that the cerium oxide abrasive thereby exhibits the highpolishing rate.

The cerium oxide particles are lower in hardness than silica particlesor alumina particles and therefore hardly make scratches on a surface tobe polished. Hence, it is useful for giving a mirror finish to a surfaceto be polished. The cerium oxide abrasive is used for, for example,polishing a glass surface.

Taking advantage of these characteristics, the cerium oxide abrasive hasbeen becoming widely used as a CMP abrasive for an insulating film of asemiconductor. This technique is disclosed in, for example, JapanesePatent Application Laid-Open No. 270402-1997. In recent years, alongwith an increase in the number of layers constituting a semiconductordevice and an increase in the degree of integration of the semiconductordevice, further increases in a yield and throughput of the semiconductordevice have been increasingly demanded. Along with that, fasterpolishing which causes no scratches has been increasingly desired in aCMP process.

However, if the cerium oxide abrasive for polishing a glass surface isused for polishing an insulating film of a semiconductor as it is,particle diameters of its primary particles are so large that visiblyobservable scratches are made on the surface of the insulating film dueto the large primary particle diameter when the surface is polished sovigorously as to attain a sufficiently high polishing rate. A decreasein the particle diameter of the primary particle can decrease thescratches but also lowers the polishing rate at the same time. In thecase of cerium oxide, it is believed that the processing is caused toproceed by its chemical action and a mechanical removing action byparticles, and the mechanical removing action by the particles causesscratches.

Thus, as a method for further decreasing scratches in a CMP processusing the cerium oxide abrasive, an abrasive improving method such as aselection of the concentration or density or particle diameters ofprimary particles of the abrasive to cause a desired polishing rate anda surface condition without scratches, or a process improving methodsuch as a reduction in a polishing pressure or a decrease in therotation speed of a surface plate may be used. However, in any of thesemethods, there arises a problem that a polishing rate lowers, and it hasbeen considered difficult to achieve a further increase in the polishingrate and a further decrease in the occurrence of the scratches at thesame time. In the future, as the number of layers constituting asemiconductor device and the degree of integration of the semiconductordevice are further increased, a polishing slurry which causes noscratches and can achieve fast polishing will be absolutely required toimprove a yield of the semiconductor device.

Recently, not only to attain a high polishing rate but also tofacilitate shallow trench isolation, a polishing slurry with a largeratio between a polishing rate for a silicon oxide insulating film and apolishing rate for a silicon nitride insulating film is demanded.Further, there has been a problem that the pH of a polishing slurrychanges with time during polishing or storage and the change in the pHlowers a polishing rate.

In addition, there has been a case where abrasive dispersed in apolishing slurry exhibit instable dispersibility by settling oragglomeration. In evaluating such dispersion stability of the polishingslurry, the dispersion stability has been difficult to evaluate innumerics since particle diameters of the dispersed particles are smalland a degree of settling cannot be recognized visually.

The present invention provides a polishing slurry whose abrasives,together with a surface to be polished such as a silicon oxideinsulating film, form a chemical reaction layer and which is capable ofpolishing the layer while achieving an increase in polishing rate and areduction in scratches at the same time, and a method of polishing asubstrate by use of the polishing slurry.

Further, the present invention provides a polishing slurry which canachieve fast polishing with good reproducibility by suppression of achange in its pH with time, has a large ratio between a polishing ratefor a silicon oxide film and a polishing rate for a silicon nitridefilm, has particles favorably dispersed therein so as to reduceoccurrences of settling and agglomeration, and has dispersibilitydetectable and controllable by a variety of optics, and a method ofpolishing a substrate by use of the polishing slurry.

DISCLOSURE OF THE INVENTION

In view of the foregoing problems, the present inventors have paidattention to polishing which takes advantage of a chemical reaction ofparticles and is performed with a mechanical action thereof minimized soas to eliminate scratches caused by the particles in a polishing slurryand have made intensive studies, thereby completing the presentinvention.

A first invention of the present invention is directed to a polishingslurry comprising particles and a medium in which at least a part of theparticles are dispersed, wherein the particles are made of at least oneof a cerium compound selected from cerium oxide, cerium halide andcerium sulfide and having a density of 3 to 6 g/cm³ and an averageparticle diameter of secondary particles of 1 to 300 nm, and atetravalent metal hydroxide.

In particular, the particles preferably have a specific surface area ofnot smaller than 50 m²/g and an average particle diameter of primaryparticles of not larger than 50 nm.

In the case where the particles are made of a tetravalent metalhydroxide, it is preferred that the particles have an average particlediameter of secondary particles of not larger than 300 nm, a density of3 to 6 g/cm³, and an average particle diameter of secondary particles of1 to 300 nm, that the particles be at least one of a rare earth metalhydroxide and zirconium hydroxide, that the hydroxide of a rare earthmetal be cerium hydroxide, and that the particles be a tetravalent metalhydroxide which is obtained by mixing a tetravalent metal salt with analkali solution.

Further, it is also preferred that the polishing slurry have a pH of 3to 9, its medium be water, and the polishing slurry contain a pHstabilizer, a dispersant and a polished surface treating agent.

The pH stabilizer preferably comprises one or more constituents, and atleast one of the constituents preferably has a pKa value which fallswithin a 1.0 unit from the pH of the polishing slurry.

The dispersant is preferably selected from a water-soluble anionicdispersant, a water-soluble cationic dispersant, a water-solublenonionic dispersant and a water-soluble amphoteric dispersant.

The polished surface treating agent is preferably a compound containingat least one atom having an unpaired electron in a molecular structureor a compound containing at least one of a nitrogen atom and an oxygenatom in a molecular structure.

Further, a ratio between a rate at which a silicon oxide insulating filmis polished by the polishing slurry and a rate at which a siliconnitride insulating film is polished by the polishing slurry ispreferably at least 5.

Still further, the polishing slurry preferably shows a lighttransmittance of not lower than 10% for light with a wavelength of 500nm when the particles are contained in an amount of 0.2% by weight, anda difference between light transmittance at a wavelength of 500 to 700nm of the polishing slurry immediately after its preparation and lighttransmittance at a wavelength of 500 to 700 nm of the polishing slurryafter it is left to stand for 24 hours is preferably not higher than20%.

Further, the polishing slurry preferably has a conductivity of nothigher than 30 mS/cm, and the particles preferably have a positive zetapotential.

A second invention of the present invention relates to a method ofpolishing a substrate by use of the polishing slurry in the firstinvention.

In particular, it is preferred that the substrate be polished with apolishing pad having a Shore D hardness of not smaller than 50, thesubstrate be a substrate in a production process of a semiconductordevice, and a silicon oxide film formed on the substrate be polished.

Further, it is preferred that the surface to be polished of thesubstrate in which at least the silicon oxide insulating film is formedand the polishing pad be moved relatively to each other while thepolishing slurry is supplied to the polishing pad on a polishing surfaceplate so as to polish the substrate, and the silicon oxide insulatingfilm is preferably polished with a polishing slurry containing particlesof a tetravalent metal hydroxide such that a polishing rate would be 200to 2,000 nm/min.

According to the foregoing polishing slurry and substrate polishingmethod according to the present invention, a surface to be polished suchas a silicon oxide insulating film can be polished quickly withoutscratching the surface. Further, a polishing rate for a silicon oxideinsulating film can be made sufficiently larger than a polishing ratefor a silicon nitride insulating film so as to selectively polish thesilicon oxide insulating film and facilitate control of a process suchas shallow trench isolation. In addition, a polishing slurry whoseparticles show good dispersibility can be obtained, dispersion stabilityof the polishing slurry can be evaluated in numerics, and the end ofpolishing and concentrations and particle diameters of the particles inthe polishing slurry can be detected and controlled by a variety ofoptical techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing one embodiment of the presentinvention which uses a CMP device.

FIG. 2 is a schematic cross sectional diagram showing an example of apolishing process of a semiconductor substrate to which the presentinvention can be applied, wherein (a) illustrates a step where trencheswere formed on a silicon substrate, (b) illustrates a step where asilicon oxide film was embedded in the trenches of (a), and (c)illustrates a step where the silicon oxide film was polished so as toseparate a device.

BEST MODE FOR CARRYING OUT THE INVENTION

As particles contained in the polishing slurry of the present invention,(1) particles of a cerium compound selected from cerium oxide, ceriumhalide and cerium sulfide and having a density of 3 to 6 g/cm³ and anaverage particle diameter of secondary particles of 1 to 300 nm or (2)particles of a tetravalent metal hydroxide are used. The particles (1)and the particles (2) may be used solely or in combination.

The cerium compound (1) in the present invention is at least onecompound selected from cerium oxide, cerium halide and cerium sulfide,and cerium oxide is preferred in that a practical polishing rate can beattained.

Further, since the cerium compound is used for polishing asemiconductor, the content of alkali metals and halogen atoms in thecerium compound is preferably not higher than 10 ppm.

To prepare the tetravalent metal hydroxide (2) in the present invention,a method of mixing a tetravalent metal salt with an alkali solution canbe used. This method is described in, for example, pages 304 and 305 of“Science of Rare Earth” (edited by Ginya Adachi, Kagaku-Dojin PublishingCo., Inc.). As the tetravalent metal salt, M(SO₄)₂, M(NH₄)₂(NO₃)₆,M(NH₄)₄(SO₄)₄ (wherein M represents a rare earth element) andZr(SO₄)₂·4H₂O are preferred, for example. A chemically active Ce salt isparticularly preferred. As the alkali solution, ammonia water, potassiumhydroxide and sodium hydroxide can be used, and ammonia water ispreferably used. Tetravalent metal hydroxide particles synthesized bythe above method can be washed so as to remove metal impurities. To washthe metal hydroxide, a method of repeating solid-liquid separation bycentrifugation several times can be used, for example.

As the tetravalent metal hydroxide, at least one of a rare earth metalhydroxide and zirconium hydroxide is preferably used. As the rare earthmetal hydroxide, cerium hydroxide is more preferred.

When the thus washed tetravalent metal hydroxide particles or the ceriumcompound particles are at least partially, preferably wholly, dispersedin a liquid medium, slurry can be prepared.

As means for dispersing the particles of the metal hydroxide or ceriumcompound in the medium, a homogenizer, an ultrasonic dispersionequipment and a ball mill can be used in addition to dispersiontreatment by a conventional agitator.

Although the slurry comprising the particles and the medium in which atleast a part of the particles are dispersed may be used as it is as thepolishing slurry of the present invention, it can be used as thepolishing slurry after a dispersant, a polished surface treating agent,a pH stabilizer, an inhibitor and the like are added as required. Thesecan be added before or after the particles are dispersed in the medium.

An average specific surface area of primary particles (hereinafterreferred to as “specific surface area of particles”) of the particles inthe polishing slurry is preferably not smaller than 50 m²/g. Further, itis preferably not larger than 500 m²/g, more preferably 80 to 500 m²/g,much more preferably 100 to 350 m²/g, particularly preferably 150 to 200m²/g. The specific surface area can be measured by a BET method based onnitrogen adsorption (for instance, trade name: AUTOSORB, products ofQUANTACHROME CO., LTD.). In this case, a sample to be measured issubjected to pretreatment at 150° C.

Further, an average of particle diameters of secondary particles(hereinafter referred to as “average particle diameter of secondaryparticles”) of the above particles dispersed in the polishing slurry ispreferably not larger than 300 nm. It is more preferably 2 to 200 nm,much more preferably 10 to 200 nm, most preferably 50 to 150 nm. Inparticular, in the case of the cerium compound particles (1), an averageparticle diameter of secondary particles must be 1 to 300 nm. When it issmaller than 1 nm, a polishing rate is apt to be low.

The particles in the polishing slurry need to cause a chemical actionwith a film to be polished. Hence, when the specific surface area issmaller than 50 m²/g, areas of the particles in which they make contactwith the film to be polished become small, thereby decreasing apolishing rate. Meanwhile, when the average particle diameter of thesecondary particles is larger than 300 nm, the areas of the particles inwhich they make contact with the film to be polished also become small,thereby decreasing the polishing rate.

In the present invention, “primary particles” refer to the smallestparticles which correspond to crystallites surrounded by gain boundariesrecognizable when observed in a powdery state by, for example, atransmission electron microscope (TEM). Further, “secondary particles”refer to agglomerations of the primary particles. In the presentinvention, the particle diameter of the secondary particle is measuredby a photon correlation spectroscopy. For example, it can be measured bymeans of ZETA SIZER 3000HS manufactured by Malvern Instruments, Ltd. orCOULTER N4SD manufactured by COULTER CO., LTD.

An average particle diameter of the primary particles of the particlesis preferably not larger than 50 nm, more preferably 0.1 to 50 nm, muchmore preferably 1 to 30 nm, particularly preferably 3 to 10 nm.

In the present invention, when a photograph of the particles is taken bya transmission electron microscope (TEM) and a primary particle(crystallite) is sandwiched between two parallel lines, a value of theshortest distance between the lines is taken as a short diameter, avalue of the longest distance between the lines as a long diameter, andan average of the shortest distance and the longest distance as the sizeof the crystallite. As the average particle diameter of the primaryparticles, an average of sizes of 100 crystallites is taken. When theaverage particle diameter of the primary particles is larger than 50 nm,a rate of occurrence of fine scratches is apt to be high, while when itis smaller than 0.1 nm, the polishing rate is liable to lower.

The particles preferably have a density of 3 to 6 g/cm³, more preferably4 to 5 g/cm³. In particular, the cerium compound particles (1) must havea density of 3 to 6 g/cm³.

When the density is lower than 3 g/m³, the effect of the particles onthe surface to be polished is weakened, and the polishing rate is liableto lower. Meanwhile, when the density is higher than 6 g/m³, it becomesdifficult to suppress occurrences of scratches. The density of theparticles is measured by, for example, a gas replacement method (forexample, trade name: ULTRAPYCNOMETER 1000, measuring device ofQUANTACHROME CO., LTD.).

The pH of the polishing slurry is preferably 3 to 9, more preferably 5to 8, particularly preferably 5.5 to 7. When the pH is smaller than 3,the efficacy of the chemical action becomes low, thereby causing adecrease in the polishing rate. Meanwhile, when the pH is larger than 9,the particle diameters of the secondary particles become large, therebycausing a decrease in the polishing rate.

As a medium in which the particles are to be dispersed, a mediumselected from the following group is suitable in addition to water.Illustrative examples of such a medium include alcohols such asmethanol, ethanol, 1-propanol, 2-propanol, 2-propyne-1-ol, allylalcohol, ethylenecyanohydrin, 1-butanol, 2-butanol(S)-(+)-2-butanol,2-methyl-1-propanol, t-butanol, perfluoro-t-butanol, t-pentyl alcohol,1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol,2,3-butanediol, 1,5-pentanediol, 2-butene-1,4-diol,2-methyl-2,4-pentanediol, glycerine,2-ethyl-2-(hydroxymethyl)-1,3-propanediol, and 1,2,6-hexanetriol; etherssuch as dioxane, trioxane, tetrahydrofuran, diethylene glycol diethylether, 2-methoxyethanol, 2-ethoxyethanol, 2,2-(dimethoxy)ethanol,2-isopropoxyethanol, 2-butoxyethanol, 1-methoxy-2-propanol,1-ethoxy-2-propanol, furfuryl alcohol, tetrahydrofurfuryl alcohol,ethylene glycol, diethylene glycol, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol monobutyl ether,triethylene glycol, triethylene glycol monomethyl ether, tetraethyleneglycol, dipropylene glycol, dipropylene glycol monomethyl ether,dipropylene glycol monoethyl ether, tripropylene glycol monomethylether, polyethylene glycol, diacetone alcohol, 2-methoxyethyl acetate,2-ethoxyethyl acetate, and diethylene glycol monoethyl ether acetate;and ketones such as acetone, methyl ethyl ketone, acetylacetone, andcyclohexanone.

Of these, water, methanol, ethanol, 2-propanol, tetrahydrofuran,ethylene glycol, acetone, and methyl ethyl ketone are more preferable,and water is particularly preferable in that a high polishing rate canbe attained.

Further, the amount of the medium is preferably 1,000 to 1,000,000 partsby weight, more preferably 10,000 to 100,000 parts by weight, based on100 parts by weight of the particles.

A pH stabilizer to be contained in the polishing slurry of the presentinvention can be selected as appropriate from those which areconventionally used as a pH buffer, such as a mixture of a carboxylicacid and its salt, a mixture of phosphoric acid and its salt, a mixtureof boric acid and its salt, and a mixture of an amine and its salt.

A preferably used pH stabilizer is one which comprises one or moreconstituents, wherein at least one of the constituents has a pKa valuewhich falls within a 1.0 unit from the pH of the polishing slurry. Forexample, to adjust the pH of the polishing slurry from 5.0 to 6.0, amixture of phosphoric acid and its salt, a mixture of acetic acid andits salt, a mixture of propionic acid and its salt, a mixture of malonicacid and its salt, a mixture of succinic acid and its salt, a mixture ofglutaric acid and its salt, a mixture of adipic acid and its salt, amixture of maleic acid and its salt, a mixture of fumaric acid and itssalt, a mixture of phthalic acid and its salt, a mixture of citric acidand its salt, a mixture of ethylenediamine and its salt, a mixture ofpyridine and its salt, a mixture of 2-aminopyridine and its salt, amixture of 3-aminopyridine and its salt, a mixture of xanthosine and itssalt, a mixture of toluidine and its salt, a mixture of picolinic acidand its salt, a mixture of histidine and its salt, a mixture ofpiperazine and its salt, a mixture of N-methylpiperazine and its salt, amixture of 2-bis(2-hydroxyethyl)amino-2-(hydroxymethyl)-1,3-propanedioland its salt, and a mixture of uric acid and its salt are suitably used.

When the pKa value does not fall within a 1.0 unit from the pH of thepolishing slurry, the pH is apt to increase over a long time period,thereby decreasing the polishing rate. The pKa value is more preferablywithin 0.5 units, much more preferably within 0.2 units, from the pH ofthe polishing slurry.

The polishing slurry of the present invention preferably contains adispersant. The dispersant may be any compound which acts on theparticles in the polishing slurry so as to reduce settling and maintaindispersibility. Inclusion of the dispersant in the polishing slurrymakes it possible to control the polishing rate or flatness of a surfaceto be polished and inhibit occurrences of scratches. The dispersant ispreferably selected from a water-soluble anionic dispersant, awater-soluble nonionic dispersant, a water-soluble cationic dispersantand a water-soluble amphoteric dispersant. They may be used alone or incombination of two or more.

Illustrative examples of the water-soluble anionic dispersant includetriethanolamine lauryl sulfate, ammonium lauryl sulfate, andtriethanolamine polyoxyethylene alkyl ether sulfate. Further, an anionicwater-soluble polymer to be described later may also be used.

Illustrative examples of the water-soluble nonionic dispersant includepolyoxyethylene lauryl ether, polyoxyethylene cetyl ether,polyoxyethylene stearyl ether, polyoxyethylene oleyl ether,polyoxyethylene higher alcohol ether, polyoxyethylene octyl phenylether, polyoxyethylene nonyl phenyl ether, polyoxyalkylene alkyl ether,a polyoxyethylene derivative, polyoxyethylene sorbitan monolaurate,polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitanmonostearate, polyoxyethylene sorbitan tristearate, polyoxyethylenesorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylenesorbit tetraoleate, polyethylene glycol monolaurate, polyethylene glycolmonostearate, polyethylene glycol distearate, polyethylene glycolmonooleate, polyoxyethylene alkylamine, polyoxyethylene hydrogenatedcastor oil, and alkylalkanolamide. Of these, the polyoxyethylenealkylamine such as polyoxyethylene octylamine is preferred.

Illustrative examples of the water-soluble cationic dispersant includecoconut amine acetate and stearyl amine acetate.

Illustrative examples of the water-soluble amphoteric dispersant includelauryl betaine, stearyl betaine, lauryldimethylamine oxide,2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine.

At least one of the dispersants is selected and added. The dispersantsare added in an amount of preferably 0.01 to 1,000 parts by weight basedon 100 parts by weight of the particles in view of dispersibility,prevention of settling, and a relationship with scratches. The amount ismore preferably 0.1 to 100 parts by weight, much more preferably 1 to100 parts by weight.

The molecular weight of the dispersant is preferably 100 to 5,000,000,more preferably 1,000 to 500,000, much more preferably 10,000 to100,000.

When the molecular weight of the dispersant is lower than 100, asatisfactory polishing rate may not be obtained at the time of polishinga silicon oxide film or silicon nitride film. On the other hand, whenthe molecular weight of the dispersant is higher than 5,000,000, theviscosity becomes high, so that storage stability of the polishingslurry may be degraded.

The polishing slurry of the present invention preferably contains apolished surface treating agent. The polished surface treating agent maybe any compound having an atom or structure capable of forming ahydrogen bond with a hydroxyl group existing on a surface to bepolished. The polished surface treating agent is preferably a compoundcontaining at least one atom having an unpaired electron in a molecularstructure or a compound containing at least one of a nitrogen atom andan oxygen atom in a molecular structure. Thereby, for example, a ratiobetween a polishing rate for a silicon oxide insulating film and apolishing rate for a silicon nitride insulating film can be made larger,which is suitable for shallow trench isolation.

Specific examples thereof include polymeric compounds such as polyvinylacetal, polyvinyl formal, polyvinyl butyral, polyvinyl pyrolidone, apolyvinyl pyrolidone-iodine complex,polyvinyl(5-methyl-2-pyrrolidinone), polyvinyl(2-piperidinone),polyvinyl(3,3,5-trimethyl-2-pyrrolidinone), poly(N-vinylcarbazole),poly(N-alkyl-2-vinylcarbazole), poly(N-alkyl-3-vinylcarbazole),poly(N-alkyl-4-vinylcarbazole), poly(N-vinyl-3,6-dibromocarbazole),polyvinyl phenyl ketone, polyvinyl acetophenone, poly(4-vinylpyridine),poly(4-β-hydroxyethylpyridine), poly(2-vinylpyridine),poly(2-β-vinylpyridine), poly(4-vinylpyridine), poly(4-vinylpyridine),poly(4-hydroxyethylpyridine), poly(4-vinylpyridinium salt),poly(α-methylstyrene-co-4-vinylpyridinium hydrochloride),poly(1-(3-sulfonyl)-2-vinylpyridiniumbetaine co-p-potassiumstyrenesulfonate), poly(N-vinylimidazole), poly(N-vinylimidazole),poly(N-vinylimidazole), poly(N-vinylimidazole), poly(N-vinylimidazole),poly(N-vinylimidazole), poly(4-vinylimidazole), poly(5-vinylimidazole),poly(1-vinyl-4-methyloxazolidinone), polyvinyl acetamide, polyvinylmethyl acetamide, polyvinyl ethyl acetamide, polyvinyl phenyl acetamide,polyvinyl methyl propionamide, polyvinyl ethyl propionamide, polyvinylmethyl isobutylamide, polyvinyl methyl benzylamide, poly(meth)acrylicacid, a poly(meth)acrylic acid derivative, a poly(meth)acrylic acidammonium salt, polyvinyl alcohol, a polyvinyl alcohol derivative,polyacrolein, polyacrylonitrile, polyvinyl acetate, poly(vinylacetate-co-methyl methacrylate), poly(vinyl acetate-co-vinyl acrylate),poly(vinyl acetate-co-pyrrolidine), poly(vinyl acetate-co-acetonitrile),poly(vinyl acetate-co-N,N-diallylcyanide), poly(vinylacetate-co-N,N-diallylamine), and poly(vinyl acetate-co-ethylene).

Further, as the polished surface treating agent, anionic compounds(hereinafter referred to as “anionic additives”) including water-solubleorganic compounds having at least one of free —COOM, phenolic —OH,—SO₃M, —O·SO₃H, —PO₄M₂ and —PO₃M₂ groups (wherein M is H, NH₄ or analkali metal atom) can also be used.

Illustrative examples of such anionic additives include the following,i.e., carboxylic acids such as formic acid, acetic acid, propionic acid,butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid,pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoicacid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoicacid, stearic acid, oleic acid, linoleic acid, linolenic acid,cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, o-toluicacid, m-toluic acid, p-toluic acid, o-methoxybenzoic acid,m-methoxybenzoic acid, pmethoxybenzoic acid, acrylic acid, methacrylicacid, crotonic acid, pentenoic acid, hexenoic acid, heptenoic acid,octenoic acid, nonenic acid, decenoic acid, undecenoic acid, dodecenoicacid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid,hexadecenoic acid, heptadecenoic acid, isobutyric acid, isovaleric acid,cinnamic acid, quinaldic acid, nicotinic acid, 1-naphthoic acid,2-naphthoic acid, picolinic acid, vinylacetic acid, phenylacetic acid,phenoxyacetic acid, 2-furancarboxylic acid, mercaptoacetic acid,levulinic acid, oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid,1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid,1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid,1,15-pentadecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid,maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconicacid, quinolinic acid, quininic acid, naphthalic acid, phthalic acid,isophthalic acid, terephthalic acid, glycolic acid, lactic acid,3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid,4-hydroxybutyric acid, 3-hydroxyvaleric acid, 5-hydroxyvaleric acid,quinic acid, kynurenic acid, salicylic acid, tartaric acid, aconiticacid, ascorbic acid, acetylsalicylic acid, acetylmalic acid,acetylenedicarboxylic acid, acetoxysuccinic acid, acetoacetic acid,3-oxoglutaric acid, atropic acid, atrolactinic acid,anthraquinonecarboxylic acid, anthracenecarboxylic acid, isocaproicacid, isocamphoronic acid, isocrotonic acid, 2-ethyl-2-hydroxybutyricacid, ethylmalonic acid, ethoxyacetic acid, oxaloacetic acid,oxydiacetic acid, 2-oxobutyric acid, camphoronic acid, citric acid,glyoxylic acid, glycidic acid, glyceric acid, glucaric acid, gluconicacid, croconic acid, cyclobutanecarboxylic acid, cyclohexanedicarboxylicacid, diphenylacetic acid, di-O-benzoyltartaric acid, dimethylsuccinicacid, dimethoxyphthalic acid, tartronic acid, tannic acid,thiophenecarboxylic acid, tiglic acid, desoxalic acid,tetrahydroxysuccinic acid, tetramethylsuccinic acid, tetronic acid,dehydroacetic acid, terebic acid, tropic acid, vanillic acid, paraconicacid, hydroxyisophthalic acid, hydroxycinnamic acid, hydroxynaphthoicacid, o-hydroxyphenylacetic acid, m-hydroxyphenylacetic acid,p-hydroxyphenylacetic acid, 3-hydroxy-3-phenylpropionic acid, pivalicacid, pyridinedicarboxylic acid, pyridinetricarboxylic acid, pyruvicacid, α-phenylcinnamic acid, phenylglycidic acid, phenylsuccinic acid,phenylacetic acid, phenyllactic acid, propiolic acid, sorbic acid,2,4-hexadienediacid, 2-benzylidenepropionic acid, 3-benzylidenepropionicacid, benzylidenemalonic acid, benzilic acid, benzenetricarboxylic acid,1,2-benzenediacetic acid, benzoyloxyacetic acid, benzoyloxypropionicacid, benzoylformic acid, benzoylacetic acid, O-benzoyllactic acid,3-benzoylpropionic acid, gallic acid, mesoxalic acid,5-methylisophthalic acid, 2-methylcrotonic acid, α-methylcinnamic acid,methylsuccinic acid, methylmalonic acid, 2-methylbutyric acid,o-methoxycinnamic acid, p-methoxycinnamic acid, mercaptosuccinic acid,mercaptoacetic acid, O-lactoyllactic acid, malic acid, leukonic acid,leucinic acid, rhodizonic acid, rosolic acid, α-ketoglutaric acid,L-ascorbic acid, iduronic acid, galacturonic acid, glucuronic acid,pyroglutamic acid, ethylenediamine tetraacetic acid, cyanide triaceticacid, aspartic acid, and glutamic acid; phenols such as phenol,o-cresol, m-cresol, p-cresol, o-chlorophenol, m-chlorophenol,p-chlorophenol, o-aminophenol, m-aminophenol, p-aminophenol,o-nitrophenol, m-nitrophenol, p-nitrophenol, 2,4-dinitrophenol,2,4,6-trinitrophenol, catechol, resorcinol, and hydroquinone; andsulfonic acids such as methanesulfonic acid, ethanesulfonic acid,propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid,hexanesulfonic acid, heptanesulfonic acid, octanesulfonic acid,nonanesulfonic acid, decanesulfonic acid, undecanesulfonic acid,dodecanesulfonic acid, tridecanesulfonic acid, tetradecanesulfonic acid,pentadecanesulfonic acid, hexadecanesulfonic acid, heptadecanesulfonicacid, octadecanesulfonic acid, benzenesulfonic acid, naphthalenesulfonicacid, toluenesulfonic acid, hydroxyethanesulfonic acid,hydroxyphenolsulfonic acid, and anthracenesulfonic acid. Further, theanionic additives may also be derivatives of the above carboxylic acidsand sulfonic acids obtained by substituting at least one of protons inthe main chain of the carboxylic acid or sulfonic acid with an atom orgroup of atoms such as F, Cl, Br, I, OH, CN and NO₂.

In addition, N-acylamino acid such as N-acyl-N-methylglycine,N-acyl-N-methyl-β-alanine or N-acylglutamic acid, polyoxyethylene alkylether carboxylic acid, acyl peptide, alkylbenzenesulfonic acid, linearalkylbenzenesulfonic acid, alkylnaphthalenesulfonic acid,naphthalenesulfonic acid formaldehyde polycondensation, melaminesulfonicacid formaldehyde polycondensation, dialkyl sulfosuccinate, alkylsulfosuccinate, polyoxyethylene alkyl sulfosuccinate, alkyl sulfoaceticacid, α-olefinsulfonic acid, N-acyl methyl taurine,dimethyl-5-sulfoisophthalate, sulfonated oil, higher alcohol sulfate,secondary higher alcohol sulfate, polyoxyethylene alkyl ether sulfuricacid, secondary alcohol ethoxy sulfate, polyoxyethylene alkyl phenylether sulfuric acid, monoglysulfate, fatty acid alkylol amide sulfate,polyoxyethylene alkyl ether phosphoric acid, polyoxyethylene alkylphenyl ether phosphoric acid, and alkyl phosphoric acid can also bepreferably used.

Further, the anionic additives may be water-soluble polymers such as apolymaleic acid, polyaspartic acid, carboxymethyl cellulose and alginicacid or derivatives thereof.

These anionic additives may be used as they are or may be used also inthe form of salts of alkali metals such as Na and K or salts of ammoniaand the like.

Of the above polished surface treating agents, polyvinyl alcohol andderivatives thereof and a polyvinyl-alcohol-based copolymer andderivatives thereof are preferably selected. Particularly, polyvinylalcohol and the derivatives thereof are preferably used. Further, apolyvinyl-alcohol-based copolymer containing (A) vinyl alcohol and (B)any one of vinyl acetate, vinyl formal, vinyl acetal, vinyl amine, vinylisobutyl ether and vinyl pyrrolidone as constituents is also preferablyused. Polyvinyl alcohol and polyvinyl pyrrolidone are more preferred.

At least one of the polished surface treating agents is selected andused. These polished surface treating agents may be added in any amountwithout particular limitations. However, in view of a relationshipbetween dispersibility of the particles in the polishing slurry andprevention of settling of the particles, the amount is preferably 0.01to 1,000 parts by weight, more preferably 1 to 300 parts by weight, muchmore preferably 10 to 100 parts by weight, based on 100 parts by weightof the particles.

Further, when the polished surface treating agents are polymericcompounds, an average molecular weight thereof is preferably 100 to5,000,000, more preferably 1,000 to 500,000, much more preferably 10,000to 100,000. When the molecular weight of the polished surface treatingagent is lower than 100, a satisfactory polishing rate may not beattained at the time of polishing the silicon oxide film or siliconnitride film, while when the molecular weight of the polished surfacetreating agent is higher than 5,000,000, the viscosity becomes high, andstorage stability of the polishing slurry may be degraded.

In addition, the polishing slurry of the present invention preferablysatisfies at least one of the following two conditions with respect tolight transmittance at a wavelength of 500 to 700 nm and a change in thelight transmittance with time.

A first condition is that the polishing slurry exhibits a lighttransmittance at a wavelength of 500 nm of not lower than 10% when 0.2%by weight of the above particles are contained in the polishing slurry.The light transmittance is more preferably not lower than 20%, much morepreferably not lower than 30%.

A second condition is that a difference between light transmittance at awavelength of 500 to 700 nm of the polishing slurry immediately afterits preparation and light transmittance at a wavelength of 500 to 700 nmof the polishing slurry after it is left to stand for 24 hours is nothigher than 20%. The difference is more preferably not higher than 10%,much more preferably not higher than 5%. When the difference is higherthan 20%, dispersion stability may be degraded. For example, when lighttransmittance at a wavelength of 500 nm of a polishing slurry is 22.3%right after its preparation and 24.7% after left to stand for 24 hours,the difference is 2.4%.

The light transmittance of the polishing slurry is measured by use oflight having a wavelength of 500 to 700 nm and can be measured by meansof, for example, a spectrophotometer U-3410 manufactured by HITACHI,LTD. If the light transmittance is 10% or higher when the particles arecontained in the polishing slurry in an amount of more than 0.2% byweight, the light transmittance is 10% or higher even if the amount ofthe particles is 0.2% by weight. To obtain a polishing slurry whichsatisfies the above light transmittance range, for example, a dispersantmay be added to the polishing slurry or the polishing slurry may besubjected to ultrasonic dispersion preferably twice or more or filteredthrough an about 1-μm membrane.

In the case of a polishing slurry having the light transmittance oflower than 10% or a polishing slurry with the higher difference in lighttransmittance as described above, particles thereof are liable tosettle, and handlings thereof are liable to be complicated. Further,wavelength of occurrences of scratches increases. In addition, when thelight transmittance is low, detection and control (for instance,detection and control of end of polishing, detection of concentration ofparticles in the polishing slurry, and the like) by various optics arenot satisfactory.

Although the concentration of the particles in the polishing slurry isnot particularly limited, it is preferably 0.01 to 5% by weight in viewof ease of handling of the polishing slurry.

The polishing slurry preferably has a conductivity of not higher than 30mS/cm. It is generally difficult to make the conductivity zero. Theconductivity is more preferably 0.01 to 10 mS/cm, much more preferably0.01 to 3 mS/cm. The conductivity can be measured by use of, forexample, a CM-20 measuring device manufactured by Toa Denshi Kogyo Co.,Ltd. When the conductivity exceeds 30 mS/cm, the particles in thepolishing slurry are liable to agglomerate, and an amount of settledparticles increases.

To obtain a polishing slurry with a conductivity of not higher than 30mS/cm, for example, in a step of mixing a tetravalent metal salt with analkali solution so as to produce metal hydroxide particles, theconcentration of the tetravalent metal salt in the mixture and the pH ofthe mixture should not be too high.

The particles dispersed in the polishing slurry preferably have apositive zeta potential. Although the zeta potential is not particularlylimited, a zeta potential of not higher than about 80 mV is sufficientfor ordinary polishing. Further, the zeta potential is more preferablynot lower than 10 mV, much more preferably not lower than 20 mV. Thezeta potential can be measured by means of, for example, a laser Dopplermethod (for example, ZETA SIZER 3000HS, product of Malvern Instruments,Ltd.). When the zeta potential is 0 mV or lower, the polishing ratelowers. It is assumed that this is because the chemical action of theparticles in the polishing slurry decreases. Further, when an absolutevalue of the zeta potential is large, the particles are not agglomeratedand settled easily, resulting in good dispersibility. To make the zetapotential positive, for example, the pH of the polishing slurry is madeequal to or lower than the isoelectric point of the particles.

The polishing method of the present invention comprises polishing asubstrate by use of the polishing slurry of the present invention. Asthe substrate, a substrate in a production process of a semiconductordevice is preferably used. Further, it is preferable to polish a siliconoxide film formed on the substrate.

As the substrate, there can be used a semiconductor substrate having asilicon oxide film and/or a silicon nitride film formed thereon, such asa semiconductor substrate having a circuit element and a wiring patternformed thereon or a semiconductor substrate having a circuit elementformed thereon.

When the silicon oxide film layer or silicon nitride film layer formedon such a substrate is polished with the above polishing slurry beingsupplied onto the layer, unevenness on the surface of the silicon oxidefilm layer can be smoothed, resulting in a smooth surface which is freefrom scratches across the substrate.

Hereinafter, the method of the present invention for polishing asubstrate when the substrate is a semiconductor substrate having asilicon oxide film formed thereon will be described. However, thepolishing method of the present invention is not limited to theparticular type of substrate.

As a polishing device, there can be used a commonly used polishingdevice which comprises a holder for holding the semiconductor substrateand a polishing surface plate having a polishing pad (or polishingcloth) attached thereon and equipped with a motor whose speed ofrotation can be changed.

FIG. 1 is a schematic diagram showing one embodiment of the presentinvention which uses a CMP device. The device of FIG. 1 has thefollowing constitution. That is, a polishing slurry 16 of the presentinvention which contains particles and a medium is supplied from apolishing slurry supply mechanism 15 onto a polishing pad 17 attached ona polishing surface plate 18. Meanwhile, a semiconductor substrate 13which has a silicon oxide insulating film 14 thereon is attached to awafer holder 11 and secured by means of a retainer 12. The silicon oxideinsulating film 14 which is a surface to be polished is brought intocontact with the polishing pad 17, and the surface to be polished andthe polishing pad are moved relatively to each other, more specifically,the wafer holder 11 and the polishing surface plate 18 are rotated,thereby carrying out CPM polishing.

The polishing pad 17 on the polishing surface plate 18 may be a generalnonwoven fabric, polyurethane foam, porous fluorine resin or the likeand is not particularly limited. Further, it is preferable that groovesin which the polishing slurry 16 accumulates be formed on the polishingpad. Conditions for polishing are not particularly limited. The rotationspeed of the polishing surface plate is preferably 100 rpm or slower soas to prevent the semiconductor substrate 13 from moving off the surfaceplate. A pressing pressure (processing load) of the semiconductorsubstrate 13 having the silicon oxide insulating film 14 which is thesurface to be polished against the polishing pad 17 is preferably 10 to100 kPa (102 to 1,020 gf/cm²) and more preferably 20 to 50 kPa (204 to510 gf/cm²) in order to attain a uniform polishing rate across thesurface to be polished and flatness of a pattern. During polishing, thepolishing slurry 16 of the present invention is continuously suppliedonto the polishing pad 17 by means of the polishing slurry supplymechanism 15 such as a pump. Although the supply mechanism and theamount of the supplied polishing slurry 16 are not particularly limited,it is preferred that the surface of the polishing pad be always coveredwith the polishing slurry.

The polishing pad for polishing the substrate preferably has a Shore Dhardness of not smaller than 50, more preferably 55 to 99, much morepreferably 60 to 95. When the pad has a Shore D hardness of smaller than50, the mechanical action of the pad tends to decrease, thereby loweringthe polishing rate. The Shore D hardness never becomes a value of 100 orlarger by definition, and when the polishing pad is too hard, scratchesmay be formed on the surface to be polished. The Shore D hardness of thepad can be measured by a Shore D hardness meter (such as “ASKER” rubberhardness meter type D, product of KOBUNSHI KEIKI CO., LTD.).

A polishing pad having a Shore D hardness of not smaller than 50 may bea foam or a non-foam such as fabric or a nonwoven fabric. As a materialof the polishing pad, resins such as polyurethane, acryl, polyester,acryl-ester copolymer, polytetrafluoroethylene, polypropylene,polyethylene, poly4-methylpentene, cellulose, cellulose ester,polyamides such as nylon and aramid, polyimide, polyimideamide,polysiloxane copolymer, oxirane compound, phenol resin, polystyrene,polycarbonate and epoxy resin can be used.

Further, fine projections are preferably formed on the surface of thepolishing pad. In addition, grooves may be formed on the surface of thepolishing pad by a variety of means.

When fine projections are formed on the surface of the polishing pad, anarea of the top surface of the projection is preferably not larger than0.25 mm², more preferably 100 mm² to 0.25 mm². When the area is largerthan 0.25 mm², the polishing rate tends to decrease, while when it issmaller than 100 μm², formation of the fine projections is difficult.

It is desirable that variations of heights of the fine projections below. The variations of the heights (1σ/average height) are preferablynot higher than 10%. When the variations of the heights (1σ/averageheight) are higher than 10%, some of the fine projections do not makecontact with the surface to be polished on the substrate at the time ofpolishing, resulting in insufficient stability of polishing properties.

An average height of the fine projections is preferably 1 to 200 μm.When the average height is larger than 200 μm, the polishing slurryflows excessively, thereby causing a decrease in the polishing rate.Meanwhile, when it is smaller than 1 μm, top surfaces of the fineprojections are liable to be adsorbed to the surface to be polished,thereby inhibiting smooth polishing. Shapes of the fine projections maybe pyramidal, conical, prismatic, cylindrical, semispherical, and thelike and are not particularly limited. Further, an average pitch of thefine projections is preferably 30 to 1,000 μm. When the average pitch issmaller than 30 μm, space between the projections is so small that thespace is clogged by scratch chippings or the like. Meanwhile, when it islarger than 1,000 μm fine projections which make contact with thesurface to be polished are so few that the polishing rate lowers.

As a method of preparing a pad having such fine projections, anembossing roll method, a metal molding method or a transfer method canbe used. Of these, the transfer method in which a pattern is transferredfrom a mold having fine pits and projections onto a photo-curing resinis preferred. A photo-curing resin composition used in the photo-curingresin layer is not particularly limited.

When a polishing pad is used in the shape of a belt, a pad in the shapeof a web is preferred. An example of the polishing pad in this shape isa polishing pad having, on a substrate layer of a biaxially stretchedpolyethylene terephthalate, a photo-curing resin layer on which fineprojections have been transferred from a mold and formed byphoto-curing.

Further, a polishing method comprising polishing with a polishing padhaving a Shore D hardness of not smaller than 50 may be applied not onlyto polishing of a silicon oxide film and the like but also to polishingof a metal film such as copper or aluminum formed on a semiconductorsubstrate.

In the polishing method of the present invention, it is preferable thatthe surface to be polished of the semiconductor substrate in which atleast the silicon oxide insulating film, e.g., a silicon oxide film, asilicon oxide film and a silicon nitride film, is formed and thepolishing pad on a polishing surface plate be moved relatively to eachother with the polishing slurry being supplied onto the polishing pad soas to polish the substrate. To cause the relative motion, in addition torotating the polishing surface plate, the holder may be rotated orrocked so as to perform polishing. Further, a polishing method in whichthe polishing surface plate is rotated in a sun-and-planet motion, apolishing method in which a polishing pad in the shape of a belt ismoved straight in a longitudinal direction or other polishing methodsmay also be used. The holder may be secured, rotated or rocked. Thesepolishing methods can be selected as appropriate according to a surfaceto be polished and a polishing device as long as a polishing pad and asubstrate are moved relatively to each other.

It is preferable that the silicon oxide insulating film be polished bysuch a polishing method such that a polishing rate would be 200 to 2,000nm/min. Particularly, it is preferable to perform polishing with apolishing slurry containing particles of a tetravalent metal hydroxideso as to achieve the above polishing rate.

Further, to perform polishing with the surface of the polishing padalways in the same condition, it is preferable to insert a step ofconditioning the polishing pad before polishing of the substrate by CMP.Preferably, for example, polishing is performed with a solutioncomprising at least water by use of a dresser having diamond particlesthereon. Then, the polishing process according to the present inventionis carried out, and then a substrate washing step comprising:

1) brush washing for removing foreign matter such as particles adheredto the polished substrate,

2) megasonic washing for replacing the polishing slurry and the likewith water, and

3) spin drying for removing the water from the surface of the substrateis carried out.

FIGS. 2(a) to 2(c) are schematic cross sectional diagrams showing anexample of a polishing process of a semiconductor substrate to which thepresent invention can be applied. FIG. 2(a) shows a step where trencheswere formed on a silicon substrate, FIG. 2(b) shows a step where asilicon oxide film was embedded in the trenches of (a), and FIG. 2(c)shows a step where the silicon oxide film was polished for deviceisolation.

For example, in the case of shallow trench isolation on a siliconsubstrate 1 in FIG. 2(a) which has a silicon nitride film 2 formedthereon and a silicon oxide film 3 embedded in trenches as shown in FIG.2(b), the silicon oxide film layer 3 is polished to the underlyingsilicon nitride film layer 2 while pits and projections on the layer 3are smoothed, thereby leaving only the silicon oxide film 3 embedded inthe device isolation portions (refer to FIG. 2(c)). In this case, when aratio between a polishing rate for silicon oxide and a polishing ratefor silicon nitride which serves as a stopper is large, a process marginof polishing becomes large.

Thus, when the silicon oxide insulating film and the silicon nitrideinsulating film are polished by use of the polishing slurry of thepresent invention, a ratio between a polishing rate for the siliconoxide film and a polishing rate for the silicon nitride film ispreferably 5 or larger. The above polishing rate ratio is morepreferably 15 to 300, much more preferably 30 to 100.

For example, when such a polished surface treating agent as describedabove is contained in the polishing slurry, the silicon oxide film isnegatively charged and the silicon nitride film has a zero potential ina neutral pH range, so that the polished surface treating agent isselectively adsorbed to the silicon nitride film. Thereby, the siliconnitride film serves as a stopper film more effectively, such apreferable polishing rate ratio as described above is attained, andmanagement of the polishing process is facilitated.

Further, when a dispersant is contained in the polishing slurry, thedispersant is adsorbed to particles in the polishing slurry and canimprove dispersion stability by a solid stabilization effect.

In addition, to use the polishing slurry for the shallow trenchisolation, it is required that it causes few scratches at the time ofpolishing. Furthermore, it can also be used in a step of flatteningimplanted metal wiring.

After the shallow trench isolation is formed on the silicon substrate bypolishing as described above, a silicon oxide insulating film layer isformed, and aluminum wiring is then formed on the silicon oxideinsulating film layer. Subsequently, a silicon oxide insulating film isformed on the aluminum wiring, and the silicon oxide insulating film isflattened by the above polishing method again. Then, a second aluminumwiring layer is formed on the flattened silicon oxide insulating filmlayer, and after formation of another silicon oxide insulating filmbetween wires and on the wiring, pits and projections on the surface ofthe insulating film are smoothed by the above polishing method, therebymaking the whole surface of the semiconductor substrate smooth. Byrepeating this procedure for a predetermined number of times, asemiconductor device having a desired number layers can be produced.

As a process for preparing an inorganic insulating film to which thepresent invention can be applied, a low pressure CVD process, a plasmaCVD process and other processes can be used. To form a silicon oxideinsulating film by the low pressure CVD process, monosilane: SiH₄ isused as a Si source, and oxygen: O₂ is used as an oxygen source. Thesilicon oxide insulating film is obtained by causing the SiH₄—O₂-basedoxidation reaction to occur at a low temperature of not higher thanabout 400° C. To dope phosphorus: P so as to accomplish surfaceflattening by high-temperature reflowing, a SiH₄—O₂—PH₃-based reactiongas is preferably used. The plasma CVD process has an advantage that achemical reaction which requires high temperatures in normal thermalequilibrium can be carried out at low temperatures. Processes ofproducing plasma are classified into capacitive-coupling type andinductive-coupling type. As a reaction gas, a SiH₄—N₂O-based gas usingSiH₄ as a Si source and N₂O as an oxygen source and a TEOS-O₂-based gas(TEOS-plasma CVD process) using tetraethoxysilane (TEOS) as a Si sourcemay be used. A substrate temperature is preferably 250 to 400° C., and areaction pressure is preferably 67 to 400 Pa. Thus, the silicon oxideinsulating film may be doped with an element such as phosphorus orboron. Similarly, to form a silicon nitride film by the low pressure CVDprocess, dichlorosilane: SiH₂Cl₂ is used as a Si source, ammonia: NH₃ isused as a nitrogen source, and the silicon nitride film is obtained bycausing the SiH₂Cl₂—NH₃-based oxidation reaction to occur at a hightemperature of 900° C. As a reaction gas used in the plasma CVD process,a SiH₄-NH₃-based gas using SiH₄ as a Si source and NH₃ as a nitrogensource can be used. A substrate temperature is preferably 300 to 400° C.

The polishing slurry and polishing method of the present invention areused for polishing not only a silicon oxide film or silicon nitride filmformed on a semiconductor substrate but also an inorganic insulatingfilm such as a silicon oxide film, glass or silicon nitride formed on awiring board having predetermined wiring, optical glass such as aphotomask, lens or prism, an inorganic conductive film such as ITO, anoptical integrated circuit constituted by glass and a crystallinematerial, an optical switching device, an optical waveguide, end facesof an optical fiber, an optical single crystal such as scintillator, asolid laser single crystal, an LED sapphire substrate for a blue laser,a semiconductor single crystal such as SiC, GaP or GaAs, a glasssubstrate for a magnetic disk, and a magnetic head. Further, thepolishing slurry and polishing method of the present invention may alsobe applied to a metal film.

EXAMPLES

Hereinafter, the present invention will be further described withreference to Examples. However, the present invention shall not belimited to these Examples in any way.

Example 1

(Preparation of Polishing Slurry)

430 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 7,300 g of pure water, and 240g of ammonia water (25% aqueous solution) was then mixed into theresulting solution under agitation so as to obtain a suspensioncontaining 160 g of cerium hydroxide (yellowish white). The obtainedcerium hydroxide suspension was subjected to centrifugation (4,000 rpm,5 minutes) so as to cause the suspension to undergo solid-liquidseparation. The liquid was removed, and pure water was then added.Centrifugation was conducted under the above conditions again. Afterthis procedure was repeated four times, the resulting suspension waswashed. When obtained particles were measured for a specific surfacearea by a BET method, it was 200 m²/g. 160 g of the particles and 15,840g of pure water were mixed together, subjected to ultrasonic dispersionand then filtered by use of a 1-μm membrane filter so as to obtain apolishing slurry with a solid content of 1% by weight. When particlediameters of particles of the polishing slurry were measured by a photoncorrelation spectroscopy, an average particle diameter of secondaryparticles was 170 nm. In addition, the pH of the polishing slurry was5.4.

(Polishing of Insulating Film Layer)

A 200-mm-φ silicon wafer on which a silicon oxide insulating film hadbeen formed by a TEOS-plasma CVD method was set in a holder of apolishing machine to which an adsorption pad for fixing a substrate wasattached. The holder was then mounted on a 600-mm-φ surface plate of thepolishing machine on which a porous urethane resin pad had been stuck,such that the insulating film surface would face the surface plate, anda processing load was set at 30 kPa (306 gf/cm²). While the abovepolishing slurry (solid content: 1 wt %) was being dripped onto thesurface plate at a rate of 200 cc/min, the surface plate and the waferwere rotated at a rotational speed of 50 rpm for 2 minutes so as topolish the insulating film. The polished wafer was then rinsed well withpure water and then dried. As a result of measuring a change in filmthickness between before and after the polishing by use of an opticalinterference-type film thickness measuring device, the change in thethickness of the silicon oxide insulating film (polishing rate: 400nm/min) was 800 nm. Further, when the surface of the insulating film wasobserved by use of an optical microscope, no distinct scratches wereobserved.

Example 2

(Preparation of Polishing Slurry)

43 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 7,300 g of pure water, and 24 gof ammonia water (25% aqueous solution) was then mixed into theresulting solution under agitation so as to obtain a suspensioncontaining about 16 g of cerium hydroxide (yellowish white). Theobtained cerium hydroxide suspension was subjected to centrifugation(4,000 min⁻¹, 5 minutes) so as to cause the suspension to undergosolid-liquid separation. The liquid was removed, and pure water was thenadded. The resulting solution was then exposed to ultrasound, therebybecoming a dispersion suspension. The obtained particles had a densityof 4.7 g/cm³ and a specific surface area of 180 m²/g. The concentrationof the particles in the dispersion was adjusted to 1.0% by weight andthe pH of the dispersion was adjusted to 6.0 so as to obtain a polishingslurry. When an average particle diameter of secondary particles in thepolishing slurry was measured by a photon correlation spectroscopy, itwas 100 nm.

(Polishing of Insulating Film Layer)

Using the thus obtained polishing slurry, a silicon oxide insulatingfilm was polished, dried and washed in the same manner as in Example 1.As a result of measuring a change in film thickness between before andafter the polishing, the change in the thickness of the silicon oxideinsulating film (polishing rate: 715 nm/min) was 1,430 nm. Further, whenthe surface of the silicon oxide insulating film was observed under anoptical microscope, no distinct scratches were observed.

Example 3

(Preparation of Polishing Slurry)

430 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 5,000 g of pure water, and 240g of ammonia water (25% aqueous solution) was then mixed into theresulting solution under agitation so as to obtain a suspensioncontaining about 160 g of cerium hydroxide (yellowish white). Thesuspension was formed into a dispersion in the same manner as in Example2. The obtained particles had a density of 4.2 g/cm³ and a specificsurface area of 240 m²/g. The concentration of the particles in thedispersion was adjusted to 1.0% by weight and the pH of the dispersionwas adjusted to 7.3, thereby obtaining a polishing slurry. When anaverage particle diameter of secondary particles in the polishing slurrywas measured by a photon correlation spectroscopy, it was 230 nm.

(Polishing of Insulating Film Layer)

Using the polishing slurry prepared by the above process, a siliconoxide insulating film was polished, dried and washed in the same manneras in Example 2. As a result, the change in the thickness of the siliconoxide insulating film (polishing rate: 401 nm/min) was 802 nm. Further,no distinct scratches were observed on the surface of the silicon oxideinsulating film.

Example 4

(Preparation of Polishing Slurry)

430 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 7,300 g of pure water, and 240g of ammonia water (25% aqueous solution) was then mixed into theresulting solution under agitation so as to obtain a suspensioncontaining about 160 g of cerium hydroxide (yellowish white). Thesuspension was formed into a dispersion in the same manner as in Example2. The obtained particles had a density of 4.5 g/cm³ and a specificsurface area of 200 m²/g. The concentration of the particles in thedispersion was adjusted to 1.0% by weight and the pH of the dispersionwas adjusted to 4.9, thereby obtaining a polishing slurry. An averageparticle diameter of secondary particles in the polishing slurry whichwas measured by a photon correlation spectroscopy was 170 nm.

(Polishing of Insulating Film Layer)

Using the polishing slurry prepared by the above process, a siliconoxide insulating film was polished, washed and dried in the same manneras in Example 2. The change in the thickness of the silicon oxideinsulating film (polishing rate: 280 nm/min) was 560 nm. Further, nodistinct scratches were observed on the surface of the silicon oxideinsulating film.

Example 5

(Preparation of Polishing Slurry)

430 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 7,300 g of pure water, and 240g of ammonia water (25% aqueous solution) was then mixed into theresulting solution under agitation so as to obtain a suspensioncontaining 160 g of cerium hydroxide. The obtained cerium hydroxidesuspension was subjected to centrifugation (4,000 rpm, 5 minutes) so asto cause the suspension to undergo solid-liquid separation. The liquidwas removed, and pure water was then added. This procedure was repeatedfour times, and then the resulting suspension was washed. When anaverage crystallite size of cerium hydroxide particles in the suspensionobtained after the washing was measured, it was 9.5 nm. Further, whenthe cerium hydroxide particles were measured for a specific surface areaby a BET method, it was 200 m²/g.

160 g of the cerium hydroxide particles and 15,840 g of pure water weremixed together, subjected to ultrasonic dispersion, and then filtered byuse of a 1-μm membrane filter so as to obtain a polishing slurry. Whenan average particle diameter of secondary particles in the polishingslurry was measured by a photon correlation spectroscopy, it was 170 nm.In addition, the pH of the polishing slurry was 5.4.

(Polishing of Insulating Film Layer)

Using the foregoing polishing slurry (solid content: 1 wt %), a siliconoxide insulating film was polished, washed and dried in the same manneras in Example 1. As a result of measuring a change in film thicknessbetween before and after the polishing by use of an opticalinterference-type film thickness measuring device, the thickness of thesilicon oxide film was decreased (polishing rate: 400 nm/min) by 800 nmby the polishing. Further, when the surface of the insulating film wasobserved by use of an optical microscope, no distinct scratches wereobserved.

Example 6

(Preparation of Polishing Slurry)

50 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 10 kg of pure water, and ammoniawater (25% aqueous solution) was then mixed into the solution underagitation such that the pH of the solution would become about 6.Thereby, a suspension containing cerium hydroxide was obtained. Theobtained cerium hydroxide suspension was subjected to centrifugation(4,000 rpm, 5 minutes) so as to cause the suspension to undergosolid-liquid separation. The liquid was removed, and pure water was thenadded. This procedure was repeated three more times, and then theresulting suspension was washed. When an average particle diameter(average crystallite size) of primary particles of cerium hydroxideparticles in the suspension obtained after the washing was measured, itwas 3.5 nm. Further, when the particles were measured for a specificsurface area by a BET method, it was 220 m²/g.

The concentration of the cerium hydroxide particles was adjusted to 0.2%by addition of water, and the pH of the suspension was adjusted to 6 byaddition of ammonia water (25% aqueous solution). The resultingsuspension was subjected to ultrasonic dispersion and then filtered byuse of a 1-μm membrane filter so as to obtain a polishing slurry. Whenan average particle diameter of secondary particles in the polishingslurry was measured by a photon correlation spectroscopy, it was 100 nm.

(Polishing of Insulating Film Layer)

A silicon oxide insulating film was polished, washed and dried in thesame manner as in Example 1 except that the above polishing slurry wasused and that the surface plate and the wafer each were rotated at 75rpm for 2 minutes. As a result of measuring a change in film thicknessbetween before and after the polishing by use of an opticalinterference-type film thickness measuring device, the thickness of thesilicon oxide film was decreased (polishing rate: 520 nm/min) by 1,040nm by the polishing. In addition, when the surface of the insulatingfilm was observed by use of an optical microscope, no distinct scratcheswere observed.

Example 7

(Preparation of Polishing Slurry)

430 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 7,300 g of pure water, and 240g of ammonia water (25% aqueous solution) was then mixed into thesolution under agitation so as to obtain 160 g of cerium hydroxide(yellowish white). The obtained cerium hydroxide was subjected tocentrifugation (4,000 rpm, 5 minutes) so as to cause the ceriumhydroxide to undergo solid-liquid separation. The liquid was removed,pure water was newly added, and centrifugation was conducted under theabove conditions again. This procedure was repeated four more times,followed by washing of the resulting cerium hydroxide. When a specificsurface area of the obtained particles was measured by a BET method, itwas 200 m²/g. Then, 16 g of the particles, 1 g of N-methylpiperazine and1,440 g of pure water were mixed together, and then commerciallyavailable nitric acid was added thereto so as to adjust the pH of themixture to 5.4. Thereafter, the mixture was subjected to ultrasonicdispersion and then filtered by use of a 1-μm membrane filter so as toobtain a polishing slurry. When an average particle diameter ofsecondary particles in the polishing slurry was measured by a photoncorrelation spectroscopy, it was 170 nm. In addition, the pH of thepolishing slurry after stored at room temperature for 4 months was 5.3.

(Polishing of Insulating Film Layer)

Using the foregoing polishing slurry (solid content: 1 wt %), a siliconoxide insulating film was polished, washed and dried in the same manneras in Example 1. As a result of measuring a change in film thicknessbetween before and after the polishing by use of an opticalinterference-type film thickness measuring device, the change in thethickness of the silicon oxide insulating film was 800 nm (polishingrate: 400 nm/min). Further, when the surface of the insulating filmafter the polishing was observed by use of an optical microscope, nodistinct scratches were observed.

Example 8

(Preparation of Polishing Slurry)

16 g of the particles obtained in Example 7 and 1,440 g of pure waterwere mixed together, and then commercially available ammonia water wasadded so as to adjust the pH of the mixture to 5.4. Thereafter, themixture was subjected to ultrasonic dispersion and then filtered by useof a 1-μm membrane filter so as to obtain a polishing slurry. When aspecific surface area of the obtained particles and an average particlediameter of secondary particles in the polishing slurry were measured inthe same manner as in Example 7, the specific surface area was 200 m²/g,and the average particle diameter of secondary particles was 200 nm.Further, the pH of the polishing slurry after stored at room temperaturefor 4 months was reduced to 4.5. When polishing of a silicon oxideinsulating film was conducted in the same manner as in Example 7, achange in the thickness of the silicon oxide insulating film was 600 nm(polishing rate: 300 nm/min). Further, when the surface of theinsulating film after the polishing was observed by use of an opticalmicroscope, no distinct scratches were observed.

Example 9

(Preparation of Polishing Slurry)

430 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 7,300 g of pure water, and 240g of ammonia water (25% aqueous solution) was then mixed into thesolution under agitation so as to obtain a suspension containing 160 gof cerium hydroxide (yellowish white). The obtained cerium hydroxidesuspension was subjected to centrifugation (4,000 rpm, 5 minutes) so asto cause the suspension to undergo solid-liquid separation. The liquidwas removed, pure water was newly added, and centrifugation wasconducted under the above conditions again. This procedure was repeatedthree more times, followed by washing of the resulting suspension. Whena specific surface area of particles in the cerium hydroxide suspensionobtained after the washing was measured by a BET method, it was 200m²/g.

Then, 16 g of the particles in the cerium hydroxide suspension, 1.5 g ofpolyoxyethylene octylamine (number average molecular weight: 10,000) and1,440 g of pure water were mixed together and then subjected toultrasonic dispersion. Thereafter, 3 g of malic acid was added to themixture, and the pH of the resulting mixture was adjusted to 5.4 byaddition of commercially available ammonia water. Then, after subjectedto ultrasonic dispersion again, the mixture was filtered with a 1-μmmembrane filter so as to obtain a polishing slurry. When an averageparticle diameter of secondary particles in the obtained polishingslurry was measured by a photon correlation spectroscopy, it was 115 nm.

(Polishing of Insulating Film Layer)

By use of the polishing slurry (solid content: 1 wt %) prepared above, asilicon oxide insulating film was polished, washed and dried in the samemanner as in Example 1. As a result of measuring a change in filmthickness between before and after the polishing by use of an opticalinterference-type film thickness measuring device, the silicon oxidefilm after the polishing showed a decrease in film thickness of 760 nm(polishing rate: 380 nm/min). Further, when the polished surface of thesilicon oxide insulating film was observed by use of an opticalmicroscope, no distinct scratches were observed.

Example 10

(Preparation of Polishing Slurry)

430 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 7,300 g of pure water, and 240g of ammonia water (25% aqueous solution) was then mixed into thesolution under agitation so as to obtain a suspension containing 160 gof cerium hydroxide (yellowish white). The obtained cerium hydroxidesuspension was subjected to centrifugation (4,000 rpm, 5 minutes) so asto cause the suspension to undergo solid-liquid separation. The liquidwas removed, pure water was newly added, and centrifugation wasconducted under the above conditions again. This procedure was repeatedthree more times, followed by washing of the resulting suspension. Whena specific surface area of particles in the cerium hydroxide suspensionobtained after the washing was measured by a BET method, it was 200m²/g.

Then, 16 g of the particles in the cerium hydroxide suspension, 6 g ofpolyvinyl alcohol (number average molecular weight: 60,000, degree ofsaponification: 96%) and 1,440 g of pure water were mixed together andthen subjected to ultrasonic dispersion. Then, the pH of the mixture wasadjusted to 5.4 by addition of commercially available ammonia water.Then, after subjected to ultrasonic dispersion, the mixture was filteredby use of a 1-μm membrane filter so as to obtain a polishing slurry.When an average particle diameter of secondary particles in the obtainedpolishing slurry was measured by a photon correlation spectroscopy, itwas 170 nm.

(Polishing of Insulating Film Layer)

By use of the polishing slurry (solid content: 1 wt %) prepared above, asilicon oxide insulating film was polished, washed and dried in the samemanner as in Example 1. As a result of measuring a change in filmthickness between before and after the polishing by use of an opticalinterference-type film thickness measuring device, the silicon oxidefilm after the polishing showed a decrease in film thickness of 800 nm(polishing rate: 400 nm/min).

Meanwhile, when a 200-mm-φ silicon wafer on which a silicon nitrideinsulating film had been formed by a low pressure CVD process wasprepared and polished in the same manner as in Example 1, the siliconnitride insulating film showed a decrease in film thickness of 20 nm(polishing rate: 10 nm/min). Thus, the ratio between the polishing ratefor the silicon oxide insulating film and the polishing rate for thesilicon nitride insulating film was 40. Further, when the polishedsurfaces of the silicon oxide insulating film and the silicon nitrideinsulating film were observed by use of an optical microscope, nodistinct scratches were observed.

Example 11

A polishing slurry was prepared in the same manner as in Example 10except that a polyvinyl pyrrolidone (number average molecular weight:about 20,000) was used in place of the polyvinyl alcohol and 1.5 g ofpolyoxyethylene octylamine (number average molecular weight: about10,000) was added. A specific surface area of particles in the polishingslurry was 220 m²/g, and an average particle diameter of secondaryparticles in the polishing slurry was 125 nm. Using this polishingslurry, a silicon oxide film formed on a surface of a silicon wafer by aTEOS-CVD process and a silicon nitride insulating film formed on asurface of a silicon wafer by a low pressure CVD process were polishedin the same manner as in Example 10. After 2-minute polishing, thechange in the thickness of the silicon oxide insulating film was 760 nm(polishing rate: 380 nm/min), and the change in the thickness of thesilicon nitride insulating film was 22 nm (polishing rate: 11 nm/min).

Further, no distinct scratches were observed on surfaces of the siliconoxide insulating film and the silicon nitride insulating film.

Example 12

(Preparation of Polishing Slurry)

200 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 18 kg of pure water, andammonia water (25% aqueous solution) was then mixed into the solutionunder agitation so as to obtain a suspension containing ceriumhydroxide. The obtained cerium hydroxide suspension was subjected tocentrifugation (4,000 rpm, 5 minutes) so as to cause the suspension toundergo solid-liquid separation. The liquid was removed, and pure waterwas then added. This washing procedure was repeated two more times. Whena specific surface area of cerium hydroxide particles in the suspensionobtained after the washing was measured by a BET method, it was 190m²/g. After the concentration of the cerium hydroxide particles wasadjusted to 1.3% by addition of water, the resulting suspension wassubjected to ultrasonic dispersion and then filtered with a 1-μmmembrane filter so as to obtain a polishing slurry. When an averageparticle diameter of secondary particles in the polishing slurry wasmeasured by a photon correlation spectroscopy, it was 105 nm.

Further, light transmittances of the polishing slurry at wavelengths of500 nm, 600 nm and 700 nm were 22.3%, 49.5% and 68.5%, respectively. Inaddition, its light transmittances at wavelengths of 500 nm, 600 nm and700 nm after the polishing slurry was left to stand for 24 hours were24.7%, 53.9% and 73.7%, respectively (differences were 2.4%, 4.4% and5.2%, respectively).

(Polishing of Insulating Film Layer)

A silicon oxide insulating film was polished, washed and dried in thesame manner as in Example 1 except that the above polishing slurry wasused and that the surface plate and the wafer each were rotated at 75rpm for 2 minutes. As a result of measuring a change in film thicknessbetween before and after the polishing by use of an opticalinterference-type film thickness measuring device, the thickness of thesilicon oxide film was decreased (polishing rate: 420 nm/min) by 840 nmby the polishing. Further, when the surface of the insulating film wasobserved by use of an optical microscope, no distinct scratches wereobserved.

Example 13

(Preparation of Polishing Slurry)

1 kg of Ce(NH₄)₂(NO₃)₆ was dissolved in 18 kg of pure water, and ammoniawater (25% aqueous solution) was then mixed into the solution underagitation so as to obtain a suspension containing cerium hydroxide. Theobtained cerium hydroxide suspension was subjected to centrifugation(4,000 rpm, 5 minutes) so as to cause the suspension to undergosolid-liquid separation. The liquid was removed, and pure water was thenadded. This washing procedure was repeated three more times.

When a specific surface area of cerium hydroxide particles in thesuspension obtained after the washing was measured by a BET method, itwas 180 m²/g. After the concentration of the cerium hydroxide particleswas adjusted to 0.2% by addition of water, the suspension was subjectedto ultrasonic dispersion and then filtered with a 1-μm membrane filterso as to obtain a polishing slurry. When an average particle diameter ofsecondary particles in the polishing slurry was measured by a photoncorrelation spectroscopy, it was 210 nm.

Further, light transmittances of the polishing slurry at wavelengths of500 nm, 600 nm and 700 nm were 14.4%, 32.7% and 48.1%, respectively. Inaddition, its light transmittances at wavelengths of 500 nm, 600 nm and700 nm after the polishing slurry was left to stand for 24 hours were24.1%, 47.9% and 65.2%, respectively (differences were 9.7%, 15.2% and17.1%, respectively).

(Polishing of Insulating Film Layer)

A silicon oxide insulating film was polished, washed and dried in thesame manner as in Example 12 except that the above polishing slurry wasused. As a result of measuring a change in film thickness between beforeand after the polishing by use of an optical interference-type filmthickness measuring device, the thickness of the silicon oxide film wasdecreased (polishing rate: 400 nm/min) by 800 nm by the polishing.Further, when the surface of the insulating film was observed by use ofan optical microscope, no distinct scratches were observed.

Example 14

(Preparation of Polishing Slurry)

100 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 18 kg of pure water, andammonia water (25% aqueous solution) was then mixed into the solutionunder agitation so as to adjust the pH of the solution to 5.5. Thereby,a suspension containing cerium hydroxide was obtained. The obtainedcerium hydroxide suspension was subjected to centrifugation (4,000 rpm,5 minutes) so as to cause the suspension to undergo solid-liquidseparation. The liquid was removed, and pure water was then added. Thisprocedure was repeated two more times so as to wash the suspension. Whena specific surface area of cerium hydroxide particles in the suspensionobtained after the washing was measured by a BET method, it was 180m²/g.

The concentration of the cerium hydroxide particles was adjusted to 0.2%by addition of water, and the pH of the suspension was adjusted to 5.5by addition of ammonia water (25% aqueous solution). Then, thesuspension was subjected to ultrasonic dispersion and then filtered witha 1-μm membrane filter so as to obtain a polishing slurry. When anaverage particle diameter of secondary particles in the polishing slurrywas measured by a photon correlation spectroscopy, it was 130 nm. Whenconductivity of the polishing slurry was measured by use of aconductivity measuring device CM-20 manufactured by Toa Denshi KogyoCo., Ltd., it was 0.5 mS/cm. When the zeta potential of the ceriumhydroxide particles was measured by use of ZETA SIZER 3000HS measuringdevise manufactured by Malvern Instruments, Ltd. in accordance with alaser Doppler method, it was 35 mV. In addition, neither agglomerationnor settling was seen.

(Polishing of Insulating Film Layer)

A silicon oxide insulating film was polished, washed and dried in thesame manner as in Example 1 except that the above polishing slurry wasused and that the surface plate and the wafer each were rotated at 75rpm for 2 minutes. As a result of measuring a change in film thicknessbetween before and after the polishing by use of an opticalinterference-type film thickness measuring device, the thickness of thesilicon oxide film was decreased (polishing rate: 440 nm/min) by 880 nmby the polishing. Further, when the surface of the insulating film wasobserved by use of an optical microscope, no distinct scratches wereobserved.

Example 15

(Preparation of Polishing Slurry)

55 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 10 kg of pure water, and ammoniawater (25% aqueous solution) was then added to the solution so as toadjust the pH of the solution to 5.5. Thereby, a suspension containing21 g of cerium hydroxide was obtained. The obtained cerium hydroxidesuspension was subjected to centrifugation (4,000 rpm, 5 minutes) so asto cause the suspension to undergo solid-liquid separation. The liquidwas removed, and pure water was then added. This procedure was repeatedthree more times so as to wash the suspension. When a specific surfacearea of particles in the cerium hydroxide suspension obtained after thewashing was measured by a BET method, it was 200 m²/g.

After the pH of the cerium hydroxide suspension (having a ceriumhydroxide content of about 0.2 wt %) was adjusted to 5.5 by addition ofammonia water (25% aqueous solution), the suspension was subjected toultrasonic dispersion and then filtered by use of a 1-μm membrane filterso as to obtain a polishing slurry. When an average particle diameter ofsecondary particles in the obtained polishing slurry was measured by aphoton correlation spectroscopy, it was 100 nm.

(Polishing of Insulating Film Layer)

A silicon oxide insulating film was polished, washed and dried in thesame manner as in Example 1 except that the above polishing slurry and anon-foamed polyurethane polishing pad having a Shore D hardness of 69were used and that the surface plate and the wafer each were rotated at75 rpm for 2 minutes. As a result of measuring a change in filmthickness between before and after the polishing by use of an opticalinterference-type film thickness measuring device, the thickness of thesilicon oxide insulating film was decreased (polishing rate: 425 nm/min)by 850 nm by the polishing. Further, when the surface of the insulatingfilm was observed by use of an optical microscope, no distinct scratcheswere observed.

Comparative Example 1

(Preparation of Polishing Slurry)

2 kg of cerium carbonate hydrate was baked at 800° C. so as to obtaincerium hydroxide. The cerium hydroxide and pure water were mixedtogether and then milled and dispersed by a bead mill. Thereafter, themixture was filtered with a 1-μm membrane filter so as to obtain adispersion. Particles had a density of 7.0 g/cm³ and a specific surfacearea of 280 m²/g. The concentration of the particles in the dispersionwas adjusted to 1.0 wt % and the pH of the dispersion was adjusted to9.1 so as to obtain a polishing slurry. When an average particlediameter of secondary particles in the polishing slurry was measured bya photon correlation spectroscopy, it was 200 nm. When lighttransmittances of the polishing slurry were measured in the same manneras in Example 12 and 13, they were about 0% regardless of wavelengths.When conductivity of the polishing slurry and zeta potential of thecerium hydroxide particles were measured in the same manner as inExample 14, conductivity was 31 mS/cm, zeta potential was −50 mV.

(Polishing of Insulating Film Layer)

By use of the polishing slurry prepared by the above method, a siliconoxide insulating film was polished, washed and dried in the same manneras in Example 2. The thickness of the silicon oxide insulating film wasdecreased (polishing rate: 191 nm/min) by 382 nm by the polishing, andsome scratches caused by the polishing were observed.

Comparative Example 2

(Preparation of Polishing Slurry)

2 kg of cerium carbonate hydrate was baked at 350° C. so as to obtaincerium hydroxide. The cerium hydroxide and pure water were mixedtogether and then milled and dispersed by a bead mill. Thereafter, themixture was filtered with a 1-μm membrane filter so as to obtain adispersion. Particles had a density of 7.0 g/cm³ and a specific surfacearea of 200 m²/g. The concentration of the particles in the dispersionwas adjusted to 1.0 wt % and the pH of the dispersion was adjusted to7.9 so as to obtain a polishing slurry. When an average particlediameter of secondary particles in the polishing slurry was measured bya photon correlation spectroscopy, it was 320 nm.

(Polishing of Insulating Film Layer)

By use of the polishing slurry prepared by the above method, a siliconoxide insulating film was polished, washed and dried in the same manneras in Example 2. The thickness of the silicon oxide insulating film wasdecreased (polishing rate: 53 nm/min) by 106 nm by the polishing, and noscratches caused by the polishing were observed.

Possibility of Industrial Utilization

As described above, the polishing slurry and the method for polishing asubstrate according to the present invention are suitable for use in aprocess of flattening a surface of a substrate by CMP, particularly aprocess of flattening an insulating film between layers, a process offorming shallow trench isolation, and other processes.

What is claimed is:
 1. A polishing slurry comprising particles and amedium in which at least a part of the particles are dispersed, whereinthe particles are made of (A) at least one of a cerium compound selectedfrom the group consisting of cerium oxide, cerium halide and ceriumsulfide and having a density of 3 to 6 g/cm³ and an average particlediameter of secondary particles of 1 to 300 nm, and (B) a tetravalentmetal hydroxide.
 2. The polishing slurry according to claim 1, whereinthe particles have a specific surface area of not smaller than 50 m²/g.3. The polishing slurry according to claim 1, wherein the particles havean average particle diameter of primary particles of not larger than 50nm.
 4. The polishing slurry according to claim 1, wherein thetetravalent metal hydroxide and has an average particle diameter ofsecondary particles of not larger than 300 nm.
 5. The polishing slurryaccording to claim 1, wherein the tetravalent metal hydroxide and has adensity of 3 to 6 g/cm³ and an average particle diameter of secondaryparticles of 1 to 300 nm.
 6. The polishing slurry according to claim 1,wherein the particles are made of at least one of a rare earth metalhydroxide and zirconium hydroxide.
 7. The polishing slurry according toclaim 6, wherein the rare earth metal hydroxide is cerium hydroxide. 8.The polishing slurry according to claim 1, wherein the particles aremade of a tetravalent metal hydroxide which is obtained by mixing thetetravalent metal salt with an alkali solution.
 9. The polishing slurryaccording to claim 1, which has a pH of 3 to
 9. 10. The polishing slurryaccording to claim 1, wherein the medium is water.
 11. The polishingslurry according to claim 1, which contains a pH stabilizer.
 12. Thepolishing slurry according to claim 11, wherein the pH stabilizercomprises one or more constituents, and at least one of the constituentshas a pKa value which falls within a 1.0 unit from the pH of thepolishing slurry.
 13. The polishing slurry according to claim 1, whichcontains a dispersant.
 14. The polishing slurry according to claim 13,wherein the dispersant is selected from a water-soluble anionicdispersant, a water-soluble cationic dispersant, a water-solublenonionic dispersant and a water-soluble amphoteric dispersant.
 15. Thepolishing slurry according to claim 1, which contains a surface treatingagent.
 16. The polishing slurry according to claim 15, wherein thesurface treating agent is a compound containing at least one atom havingan unpaired electron in a molecular structure or a compound containingat least one of a nitrogen atom and an oxygen atom in a molecularstructure.
 17. The polishing slurry according to claim 1, wherein aratio between a polishing rate for a silicon oxide insulating film and apolishing rate for a silicon nitride insulating film is at least
 5. 18.The polishing slurry according to claim 1, which shows a lighttransmittance of not lower than 10% at a wavelength of 500 nm when theparticles are contained in an amount of 0.2% by weight.
 19. Thepolishing slurry according to claim 1, wherein a difference betweenlight transmittance at a wavelength of 500 to 700 nm of the polishingslurry immediately after its preparation and light transmittance at awavelength of 500 to 700 nm of the polishing slurry after it is left tostand for 24 hours is not higher than 20%.
 20. The polishing slurryaccording to claim 1, which has a conductivity of not higher than 30mS/cm.
 21. The polishing slurry according to claim 1, wherein theparticles have a positive zeta potential.
 22. A method of polishing asubstrate with the polishing slurry according to claim
 1. 23. The methodof claim 22, wherein the substrate is polished with a polishing padhaving a Shore D hardness of not smaller than
 50. 24. The method ofclaim 22, wherein the substrate is a substrate in a production processof a semiconductor device.
 25. The method of claim 22, wherein a siliconoxide film formed on the substrate is polished.
 26. The method of claim22, wherein the polishing slurry which is supplied to the polishing padon a polishing surface plate, and the substrate which comprises asilicon oxide insulating film are moved relatively to each other so asto polish the substrate.
 27. The method of claim 26, wherein the siliconoxide insulating film is polished with a polishing slurry containingtetravalent metal hydroxide particles such that a polishing rate wouldbe 200 to 2,000 nm/mm.
 28. The polishing slurry according to claim 2,wherein the particles have an average particle diameter of primaryparticles of not larger than 50 nm.
 29. The polishing slurry accordingto claim 28, wherein the tetravalent metal hydroxide has an averageparticle diameter of secondary particles of not larger than 300 nm. 30.The polishing slurry according to claim 29, wherein the tetravalentmetal hydroxide has a density of 3 to 6 g/cm³ and an average particlediameter of secondary particles of 1 to 300 nm.
 31. The polishing slurryaccording to claim 30, wherein the particles are made of at least one ofa rare earth metal hydroxide and zirconium hydroxide.
 32. The polishingslurry according to claim 31, wherein the particles are made of atetravalent metal hydroxide which is obtained by mixing the tetravalentmetal salt with an alkali solution.
 33. The polishing slurry accordingto claim 32, which has a pH of 3 to
 9. 34. The polishing slurryaccording to claim 33, which contains a pH stabilizer.
 35. The polishingslurry according to claim 34, which contains a dispersant.
 36. Thepolishing slurry according to claim 35, which contains a polishedsurface treating agent.
 37. The polishing slurry according to claim 36,wherein a ratio between a polishing rate for a silicon oxide insulatingfilm and a polishing rate for a silicon nitride insulating film is atleast
 5. 38. The polishing slurry according to claim 37, which shows alight transmittance of not lower than 10% at a wavelength of 500 nm whenthe particles are contained in an amount of 0.2% by weight.
 39. Thepolishing slurry according to claim 38, wherein a difference betweenlight transmittance at a wavelength of 500 to 700 nm of the polishingslurry immediately after its preparation and light transmittance at awavelength of 500 to 700 nm of the polishing slurry after it is left tostand for 24 hours is not higher than 20%.
 40. The polishing slurryaccording to claim 39, which has a conductivity of not higher than 30mS/cm.
 41. The polishing slurry according to claim 40, wherein theparticles have a positive zeta potential.
 42. A method of polishing asubstrate with the polishing slurry according to claim
 41. 43. Themethod of claim 42, wherein the substrate is a substrate in a productionprocess of a semiconductor device.
 44. The method of claim 43, wherein asilicon oxide film formed on the substrate is polished.